A Beginner’s Guide To GPS Navigation (Part 2)
A Beginner’s Guide To GPS Navigation (Part 2)
How Does Your GPS Work?
The main purpose of your portable GPS unit is to tell you precisely where on earth you are at that particular moment. This device can do this by triangulating your position based on information it receives from GPS satellites orbiting the earth.
With signals coming from three satellites, your portable GPS unit can calculate and tell you your 2D location in terms of latitude and longitude (will get to these terms in a moment). With four or more satellite signals, your GPS device can tell you more information about your position including how high you are from sea level – or what is technically called altitude.
Once your portable GPS unit locks in your position, it can then track your movement as well as give a whole bunch of other information like your speed, bearing, distance to your destination and more. Oh yes, it can also play your favorite MP3 files while you’re at it.
Now lets take a look at how your GPS communicates with you:
The GPS Whisperer
If you are buying a GPS for yourself, as a gift or are planning on reselling them, then understanding what the information that they give to you means is really important and helpful.
Some of the terms can seem rather technical, but once you know it’s so easy to remember, so let’s count down through them:
- Longitude: There is an imaginary line running from the North to the South Pole which passes through Greenwich, England. This line is called the Prime Meridian. An incremental distance measured in degrees from the east or west of this line is called the longitude.
- Latitude: Just like the Prime Meridian, the Equator divides the world into a northern and southern hemisphere. Measured distances either on the north or the south of the equator is called latitude.
- Elevation: Your elevation is a measure of your distance, either above or below, the mean sea level.
- Multipath Error: GPS signals can sometimes bounce off tall buildings and mountains before these signals can ever reach your portable GPS receiver. This would cause problems in the accuracy of the signals you receive resulting in multipath errors.
- C/A Code: Civilian users of portable GPS receivers like you receives standard positioning signals called Coarse/Acquisition Code or more commonly called C/A Code. These signals can give your fix position with an accuracy of 100 meters or less.
- L1: There are two radio frequencies transmitted by GPS satellites and the first one called L1 transmits at 1575.42 Mhz and carries the C/A Code, P-Code and other nav messages.
- L2: The second set of radio frequencies from GPS satellites transmits at 1227.6 MHz and carries only the P-Code.
- OS: Just like a basic computer, the basic software that controls your portable GPS receiver runs through a specific Operating System or OS.
- Cracked Software: Your portable GPS device functions with the use of a GPS software. This software is licensed and sold by manufacturers. Hackers can sometimes remove the security coding placed by software manufacturers, resulting in cracked software. This is mostly prevalent in portable GPS units sold by Chinese traders.
- Assisted GPS: To boost the performance of portable GPS systems, cell phone networks can be utilized using Assisted GPS or AGPS.
- Warm Start Up Time: This is the time it takes for the portable GPS receiver to start navigation using the information during your last use, which is stored up in its memory.
- Cold Start Up Time: This is the time it takes for the portable GPS receiver to start providing position updates even without store information in its memory from previous use.
- Maximum Positional Altitude: This is the maximum altitude where your portable GPS receiver can function accurately and give you accurate coordinates. Some portable units like GPS watches can have its maximum elevation set by the user. The unit will alarm once the set altitude is reached, as in the case of mountain hikes and climbing.
- Recapture Time: This is the time it takes for the unit to recover and interrupted signal without powering your unit off.
- Position Sensitivity: This sensitivity determines how fast your unit can search and process GPS signals to give you an accurate fix of your location.
- Data Update Rate: One thing that you should remember as a portable GPS device user is to have updated maps and other directional information in your unit. How fast your unit can update information depends on its data update rate. Higher-end models have auto update features that updates live traffic feed every 5 minutes for more accurate driving information.
If you learn what these terms mean you’ll soon be able to decipher the information that your GPS is giving to you. If you are using software like google maps, then it will be useful indeed to be able to enter longitude and latitude and find the position that your GPS has been displaying.
The Usual Suspects
Chinavasion has a whole range of great value GPS devices that can save you loads of money over the name brands that you see on the high street whilst giving you exactly the same functionality!